Method of making a reconstituted tobacco sheet



United States Patent- O 3,409,028 METHOD OF MAKING A RECONSTITUTED TOBACCO SHEET Roger Zygmunt de la Burd, Richmond, Va., assignor to Philip Morris Incorporated, New York, N.Y., a corporation of Virginia No Drawing. Filed Dec. 17, 1965, Ser. No. 514,714

2 Claims. (Cl. 131140) ABSTRACT OF THE DISCLOSURE This disclosure relates to method of preparing a reconstituted tobacco sheet which includes tobacco stems, fines and midribs, such method involving the expanding or putting of the tobacco stems, grinding the stems and mixing them with a liquid vehicle to form a slurry, casting or rolling the slurry into a sheet and evaporating the liquid.

This invention relates to a method of preparing a tobacco product. More particularly, the present invention relates to a novel method for making a reconstituted tobacco sheet produce which includes puffed stems. As use herein, stems includes tobacco stems, veins and mid-ribs.

Many methods have been employed for the preparation of reconstituted tobacco products, whereby tobacco fines, dust and midribs are combined with a binder to form a coherent sheet which resembles leaf tobacco and which is commonly referred to as reconstituted tobacco. However, the sheet which is produced by the presently known methods lacks some of the desirable qualities of natural leaf tobacco. The physical properties of such sheets are inferior to those of the natural leaf. For example, they lack the thickness or hand of tobacco leaf and are characterized by less tensile strength and less elastic properties as well. Considerable dusting or deterioration of the reconstituted product is also experienced. To overcome these deficiencies, humectants and plasticizers have been added to the reconstituted sheets in order to improve their mechanical properties. However, the resulting sheets still have been found to exhibit smoking characteristics inferior to the natural leaf. It is not possible, therefore, to use the reconstituted tobacco alone and it must be included in a cigarette with a greater proportion of natural tobacco to give an acceptable product. One of the Serious difficulties encountered is the noticeable presence of even small amounts of the tobacco stem in the final product. On occasion, sharp ends from stem pieces puncture the cigarette paper.

Reconstituted tobacco sheets are conventionally prepared by grinding tobacco products into nonfibrous colloidal suspensions which are then cast into sheets. The sheets are allowed to stand to permit evaporation of the colloid vehicle and a sheet approximating the characteristic of tobacco leaf results. Various methods have been attempted to eliminate some of the above-mentioned disadvantages of reconstituted tobacco sheets. For example, in U.S. Patent #2,656,841, issued to Gurley, a process is described whereby a conventional tobacco sheet is cast and then subjected to intense heat in order to expand or 3,409,028 Patented Nov. 5, 1968 puff portions of the sheet. The sheet thus obtained, however, possesses a somewhat limited filling power and nonuniformity in stem-material is carried over into the final product. A further disadvantage resulting from puffing the entire sheet after casting is that the stem material either does not puif to its full potential volume or the surrounding leaf material is damaged due to excessive heat when an attempt is made to fully puff the stem material in the cast sheet. To obtain an acceptable product, additives are required and these ultimately impair the smoking taste. Because the sheets are cast before pufling, they exhibit the organoleptic properties of conventional sheets. Thus, a real need exists in the industry for a process which will yield a reconstituted tobacco sheet free of additives, having the physical properties and smoking characteristics of the natural tobacco leaf.

In accordance with the present invention, a method has been discovered whereby tobacco stems are expanded or puffed before being incorporated into a reconstituted sheet. It has been found that sheets prepared from such puffed stems are physically and chemically superior to sheets known heretofore. No additives or binders are required to obtain a sheet with good wet strength. The puffed stems have the advantage of being more readily ground to pulp than untreated stems. A more uniform colloidal suspension is thus obtained. The viscoelastic properties of the colloid are superior and permit the use of a more concentrated casting slurry. This obviates the necessity for evaporating large amounts of liquids thereby decreasing the drying time which is the time determining factor in the process of preparing reconstituted tobacco sheet. A more efiicient and less costly operation results from the use of a highly concentrated casting slurry. The instant process thus presents a significant advance over known methods in its lower. cost, greater speed of operation and improved pyrolytic and organoleptic properties.

The present invention comprises the following steps.

Tobacco stems, of any variety, either bright or burley, although most preferably of the bright variety, are expanded or puffed by a convenient process preferably by exposing them to radiant heat or microwave energy under certain conditions as set forth in copending applications Nos. 514,667, 514,699 and 516,112, entitled Tobacco Stems Puffed by Radiant Energy and Method for Preparing Same, Tobacco Stems Puifed by Microwave Energy and Method for Preparing Same and Combined Air Separation and Pufiing Process, respectively, and file-d of even date herewith. The puffed stems are preferably stabilized to prevent reversion to their former unpuffed dimensions as outlined in copending application, Ser. No. 514,698 entitled Methods To Prevent Shrinkage of Puffed Tobacco Products and might be sliced according to the method taught in copending application, Ser. No. 514,720 entitled Sliced Pufi'ed Stems in Cigarette Filler and Method for Making Same, both of which are'filed of even date herewith.

The puffed sliced or unsliced stems may then be ground and mixed with a vehicle, such as water, to form a casting slurry. The slurry in either case exhibits vastly improved visco-elastic properties over those of the prior art methods in that it-is'much less viscose than the casting slurry made from unpuifed stems. The slurry is then cast or rolled intosheet form, preferably with castingor paper Example 1 Three batches of bright stems, approximately one pound each, were puffed in a muflie furnace, under quartz lamps, andby microwaves, respectively. The first batch was held at-300 C. for 32 seconds in a muffle furnace manufactured by Thermo Electric Manufacturing Co., Dubuque, Iowa; the second batch was exposed to two 1000 watt G.E. Type T quartz lamps for 35 seconds at a distance of 3 inches; and the third groupwas placed in a Raytheon Mark V microwave oven operating at 2,450 mc. for 28 seconds. Each sample was then ground dry in a Waring Blendor and mixed with water to give a castable consistency. For puffed stems it was necessary to add approximately'450 mls. of water per 110 grams of stems whereas the unpulfed control stems processed in similar manner required twice the amount of water to obtain a similar consistency adequate for casting sheets. The resulting sheets were comparable with sheets made from unputfed stems but were easier to dry and were more flexible. Due to the fact that the visco-elastic properties of the slurries had changed and less water was needed, the drying time was reduced by approximately 40% Sheets from treated bright tobacco stems were much easier to dry since a substantially smaller amount of liquid had to be evaporated from the same area of the sheet. The high solid content of the slurry allowed also greater output of the equipment for sheet manufacture.

It was observed that it was impossible to cast an acceptable sheet from bright stems not first subjected to cooking in phosphates or inorganic bases. However, the stems puffed with radiant heat could be cast directly into sheets after 5 minutes grinding in liquid, preferably water, One of the advantages of the treatment was that the sheet from the treated stems did not have a glossy appearance as did sheets prepared by known methods. The sheets were cut by hand and cigarettes made from them were evaluated by a panel of 17 experts. Cigarettes from treated sheets were judged to have less objectionable sidestream odor, and more aromatic and milder mainstream smoke.

Example 2 Three samples of mixed bright tobacco stems each averaging 350 grams in weight were exposed to a temperature of 360 C. for 60 seconds in a muffie furnace of the type used in Example 1. The stems were subsequently ground, in 1:1 proportion with water, in a Waring Blendor for 7 minutes. An aliquot containing approximately one-half of the starting material was used for preparing cast sheets. The sheets were allowed to dry at 60% RH. and 74 C. for approximately three days. The remaining starting material was subsequently homogenized in a Manton-Gaulin pressure valve homogenizer. The pressure was adjusted to 5000 p.s.i. at the orifice and the homogenization time was minutes, For comparison, the control, an untreated sample of mixed bright stems, underwent an identical grinding and homogenization treatment. Subsequently, sheets were cast from both of the materials. The sheets from ground-homogenized but untreated mixed bright stems, sheets from treated ground and homogenized stems, and the sheets from treated ground stems without homogenization were compared on Instron equipment for their work strength. The resultssummariz ed in Table 1 show that the puffing treatment improved the handling proper ties and work factor of the sheets.

TABLE 1.WORK FACTOR [Work (gm. cm./in.

Sheets Cast Sheets Cast Sheets Cast From Unpufled Percent Moisture From Pufied From Unputled Stems-Carm the Sheet Homogeuized Homogenized boxymethyl Stems Stems Cellulose Binder 30 20 10 4 26 10 20 24 ll 25 21 .39 1r 30 19 '47 1 ''15 e 40 1s 52 ;17 15 so a2 .45 14 132 a5 43 13 162 40 42' The sheets from puifed stems without homogenization were substantially stronger than the s'heets from untreated stems even if homogenized. The sheets from puffed and homogenized stemswe're, on the other hand, even stronger than the sheets made from the same material without homogenization. The viscosity of the solution of treated and untreated stemseven after homogenization differed substantially. This again allowed the use of substantially higher solid content in the casting of sheets and the production output of the equipment was substantially increased. The difference was evident on comparing the viscosities of 100 g. samples of bright stems treated and homogenized in 100 ml. of water versus the identical untreated sample. The measurements were performed on a 'Brooks viscosimeter. The viscosity of treated-homogenized samples was 400 centipoises and the viscosity of the untreated homogenized sample was 24,300 centipoises. This indicates that in the samples including puffed stems the homogenization did not significantly alter the viscose properties of the slurry,whereas in the untreated stem sample the homogenization lowered substantially the viscosity of the slurry. In spite of this lowering in viscosity, the slurry from the radiantly treated stems had times lower viscosity than that of the slurry of the control which resulted in a better product produced at lesser expense.

Example 3 I Mixed bright stems puffed for -30 .seconds-in a muflie furnace like that in Examples 1 and 2 were ground in excess water in a Waring Blendor. Occasionally new stems were added until the suspension had a consistency judged to be castable into sheets. This final consistency was 4:1, four parts of water+5% glycerine for every part of stems. To obtain a satisfactory consistency of slurry from unpuifed stems ground in similar manner, twice the amount of-liquid was required. Subsequently, this slurry was passed twice through a homogenizer (Mauton-Gaulin) for 15 minutes at about 8,000 lbs./in. For comparison of wet strength, sheets were cast from slurries of unpulfed stems and the same slurries using carboxymethylcellulose binder, ammonium phosphate solubles, and others. All of the sheets were dried at standard conditions and evaluated for physical characteristics and smoke. The sheets prepared from puffed stems were always superior in physical properties 'and had significantly improved wet strength (.Table 2).

TABLE 2.--WET STRENGTH" The cigarettes prepared from the pulled stem sheets Example 4 Mixed bright stems were radiantly putfed by exposure to two 1000 watt quartz lamps for 45 seconds at 3 inches. Then the stems were imediately spread on separators set at a gap distance of 0.03 inch. The spread stems were cut into filler without separation of the dust formed on spreading. Subsequently, the cut filler was sieved and the 140 mesh fraction was separated on a Sweco separator. This dust was mixed with water in a 1:4 ratio to make a suitable slurry (5% glycerine was added) and the slurry was then dispersed in a Waring Blendor for 6 minutes. No homogenization followed. The sheets were cast manually with ease and then were air dried for 48 hours at 73 F. and 60% relative humidity. The sheets were of good quality and were easily removed from the plates. The plates measured 24 x 9 inches. The sheets were judged superior in all physical aspects to sheets made from the unpuifed control stems (untreated ground). The aroma and smoke were judged by a panel of 17 experts to be improved over that of the sheets prepared from unpuffed stems.

Example 5 240 grams of mixed bright pulfed stems prepared as in Example 4 were ground for 3 minutes in a Waring Blendor and the 990 ml. of water was added and ml. of glycerine. The unputfed stems required the addition of 2200 m1. of water. Both slurries were passed twice through a Manton-Gaulin homogenizer for 20 minutes at 8000 lbs./in. Both homogenized slurries were examined for their viscosities on a Brooks viscometer. At equal float ratios, the viscosity of nonpuffed stems slurry was 153.3 centipoises as compared with the 24.3 centipoises for the slurry from puffed stems.

Sheets were cast manually and cut into filler by a standard process. Standard blend cigarettes, containing 20% of these sheets, were prepared. The cigarettes prepared from puffed stem sheets were compared by a panel of 23 experts with the control. They were judged less washed out, less bitter, and more aromatic. The wet strength of the sheets from puffed stems Was 40 to 200% greater than that of the control at moisture contents between and 35% as determined on Instron equipment.

Example 6 Stems were treated by radiant heat as described in Example 4, and then compared as to mechanical proper- 6 ties by determining the ease of grinding in the Waring Blendor. Puifed stems at two difierent levels of moisture both were more susceptible to grinding than the unpufled control (Table 3).

TABLE 3.GRINDABILITY 0F STEMS [Percent of sample larger than 40 mesh] On the basis of visual observation and sieve tests it appeared that a more uniform distribution of particle size was obtained from puifed stems thus making the material better for casting uniform sheets.

The sheets from the treated homogenized bright stems also had better handling characteristics and better flexibility than the control sheet.

The cast sheets were evaluated organoleptically and were judged to be more aromatic, sweeter, less green, and more desirable. The sheets were cut at 45 cuts/inch, and the cigarettes made therefrom were judged as milder, sweeter, and with more body. Sidestream smoke was also evaluated by a 20-member panel, and a statistically significant preference was expressed at a confidence level of p 0.05 for the cigarettes made from the treated homogenized stems as compared with a control. The smoke composition was also analyzed on a Consolidated Electrodynamics Corp. Mass Spectrograph, Model 21-103B, and it was found that the cigarettes made from the high solid slurries from treated bright stems delivered somewhat less gas phase constituents and up to 50% less total particulate matter than the control.

Iclaim:

1. The method of making a reconstituted tobacco sheet having good workability and wet strength which comprises the steps of pufling tobacco stems, reducing the pufied stems to a fine mesh, mixing the resultant stem particles with water to form a slurry, casting the slurry and finally evaporating the water to form a coherent reconstituted tobacco sheet.

2. The method of claim 1 in which the pufied stems are reduced to particle size by a wet grinding operation.

References Cited UNITED STATES PATENTS 2,739,599 3/1956 Abbott 131121 MELVIN D. REIN, Primary Examiner. 

